Conventionally, porous resin particles (specifically, acrylic-based cross-linked resin particles and styrene-based cross-linked resin fine particles) are commonly used, for example, as additives to external preparations such as cosmetics and additives to coating agents such as coating materials (e.g., matting agents for coating materials); light diffusion agents for light diffusion members such as illumination covers and light diffusion plates, and for optical films such as light diffusion films and glare-proof films in liquid crystal display apparatuses; blocking preventing agents for films; and the like.
For example, light diffusion members such as illumination covers and light diffusion plates containing the porous resin particles as a light diffusion agent are manufactured by mixing the resin particles as a light diffusion agent in a base material resin, and subjecting the resulting resin composition to molding such as extrusion molding or injection molding.
As a method of manufacturing porous resin particles, for example, Patent Documents 1 to 4 disclose methods in which a monomer mixture containing a monofunctional monomer such as (meth)acrylic acid or (meth)acrylic acid ester and a cross-linkable ethylenic monomer having 2 or more vinyl groups (crosslinking agent) is subjected to suspension-polymerization in the presence of a polymerization initiator and an organic solvent as a pore forming agent, after which the pore forming agent is removed. Furthermore, Patent Document 5 discloses a method in which polymer seed particles manufactured with styrene, (meth)acrylic acid ester, or the like are caused to absorb a cross-linkable monomer and a polymerization initiator, after which the cross-linkable monomer is polymerized, and, thus, a polymer (porous resin particles) having a composition different from that of the original polymer particles is obtained.